Put pork, orange juice, lime juice, stock, garlic, oregano, cumin, salt and pepper in a 6-quart electric pressure cooker. Lock the lid and cook on HIGH pressure for 55 minutes, then allow a 20-minute natural release before releasing the remainder according to the appliance instructions.
Check that the pork separates easily with a fork; pressure-cook for 10 minutes more if still firm. Lift out, discard large fat seams and pull into broad pieces.
Skim the cooking liquid. Toss pork with 1/4 cup of it, spread on a sheet pan and broil 6 inches from the element for 4 to 6 minutes until the edges brown, turning once.
Cut the loaf into four 6-inch portions and split each horizontally. Spread cut faces with mustard, then layer with ham, salami, warm pork, Swiss and drained pickles.
Close sandwiches and spread butter thinly over their outsides. Heat a large skillet over medium-low heat and cook two at a time under a second heavy skillet for 4 to 5 minutes per side.
Check that the cheese has melted and the center reaches 165°F, reducing the heat and continuing if needed. Cut each sandwich diagonally and serve immediately.